Urethane-acrylic coatings for optical fiber

ABSTRACT

The present invention relates to a method of improving the tensile, elongation, and/or modulus (overall toughness) of a radiation curable composition by reacting in a free multi-functional isocyanate prior to curing.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of commonly owned copending U.S.application Ser. No. 10/042,382, filed on Jan. 11, 2002 (now allowed),which claims the benefit of U.S. provisional application 60/260,915which was filed on Jan. 12, 2001, and which is hereby incorporated inits entirety by reference.

FIELD OF THE INVENTION

The present invention relates, inter alia, to fiber optic coatingcompositions having improved toughness. Furthermore, the presentinvention relates to a method of improving the tensile, modulus, and/orelongation of a radiation curable coating composition by adding a freeisocyanate.

BACKGROUND OF THE INVENTION

In the production of optical fibers, a resin coating is appliedimmediately after drawing of the glass fibers for protection andreinforcement of the glass fiber. Generally, two coatings are applied, asoft primary coating layer of a flexible resin (low modulus and low Tg)which is coated directly on the glass surface and a secondary coatinglayer of a rigid resin (higher modulus and higher Tg) which is providedover the primary coating layer. Often, for identification purposes, thefibers will be colored. Accordingly, the fibers may further be coatedwith an ink, which generally is a curable resin comprising a colorant(such as a pigment and/or a dye), or the secondary coating may be acolored secondary coating (i.e., comprise a colorant).

Several coated (and optionally inked) optical fibers can be bundledtogether to form a so-called optical fiber ribbon, e.g., four or eightcoated (and optionally inked) optical fibers are arranged on a plane andsecured with a binder to produce a ribbon structure having a rectangularcross section. Said binder material for binding several optical fibersto produce the optical fiber ribbon structure is called a ribbon matrixmaterial. In addition, a material for the further binding of severaloptical fiber ribbons to produce multi-core optical fiber ribbons iscalled a bundling material.

Resins that cure on exposure to radiation such as ultraviolet radiationare favored in the industry, due to their fast cure, enabling the coatedfiber to be produced at high speed. In many of these radiation curableresin compositions, use is made of urethane oligomers having reactiveterminal groups (such as an acrylate or methacrylate functionality,herein referred to as (meth)acrylate functionality) and a polymerbackbone. Generally, these compositions may further comprise reactivediluents, photoinitiators, and optionally suitable additives.

It is a continual objective of the industry to improve the performanceof the coatings. Among the many performance characteristics required ofthe coating systems, the tensile strength, modulus and elongation areimportant. Accordingly, formulators add components to the composition tomanipulate these characteristics.

The applicants have discovered that they can introduce a freemulti-functional isocyanate either directly mixed with themulti-functional acrylate or into the final composition, prior tocuring, and thereby improve tensile, elongation, and/or modulusproperties, in the composition. Applicants have furthermore discoveredthat the addition of relatively small amounts of aromatic urethaneacrylate components can also give improved mechanical properties.

SUMMARY OF THE INVENTION

The present invention provides a method of improving the tensile,elongation, and/or modulus (overall toughness) of a radiation curablecomposition by reacting in a free multi-functional isocyanate prior tocuring.

The present invention further provides a method of improving thetensile, elongation, and/or modulus (overall toughness) of a radiationcurable composition by having relative small amounts aromatic urethaneacrylate components present.

In addition, the present invention provides compositions comprising

-   -   (i) a component according to the following formula (a)        A-X₁-A  (a)    -    wherein        -   A represents a (meth)acrylate group; and        -   X₁ represents an aliphatic or aromatic group; and    -   (ii) a urethane (meth)acrylate component comprising a        (meth)acrylate group, X₁, and a residue of a multifunctional        isocyanate.

The inventors have found, that the components as supplied by rawmaterial manufacturers, often comprise undesired by-products orside-products (“impurities”), which may lessen one or more of theeffects the components are supposed to accomplish. For instance,multi-functional acrylate components (such as ethoxylated Bisphenol Adiacrylate) often are inclusive of minor amounts of monofunctionalacrylates (such as ethoxylated Bisphenol A mono acrylate) which effectthe overall performance properties of the coatings. The presentinvention comprises the step of converting at least a portion of themono-functional components to multi-functional components, and therewithimprove properties.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

Multi-functional refers to a compound having at least two functionalgroups. For example, multifunctional acrylate or multi-functionalisocyanate refers to an acrylate or an isocyanate compound having atleast 2, preferably 2-3, acrylate or isocyanate groups, respectively.

The radiation-curable composition of present invention may be formulatedusing any suitable components and processes used for such purposes.Typcially, the coatings will be (meth)acrylate radiation curablecompositions preferably having, relative to the total weight of thecomposition, more than 90% acrylate-functional components.

The radiation curable composition preferably comprises a radiationcurable oligomer and a radiation curable diluent. Each of the componentsmay be mono or polyfunctional, poly meaning 2 or more functional.Generally, the functionality of the radiation curable components is 12or lower. Preferred functionality for at least one of the components ison average 1.8-4.

The terms diluent and oligomer are used in this specification to denotea compound with lower, respectively, higher viscosity. The oligomergenerally will have a molecular weight of about 400 or higher and anaverage functionality of about 1.2 or higher, preferably an averagefunctionality of about 1.8-4.

The reactive diluent has a viscosity that is lower than the viscosity ofthe oligomer. In case an oligomer is used with high viscosity, thediluent may have a molecular weight up to about 700.

(A) Oligomer

Generally, optical fiber coating materials comprise as an oligomer aurethane acrylate oligomer, comprising an acrylate group, urethanegroups and a backbone. The backbone is derived from a polyol which hasbeen reacted with a diisocyanate and hydroxyalkylacrylate. However,urethane-free ethylenically unsaturated oligomers such as polyesteracrylates may also be used.

Examples of suitable polyols are polyether polyols, polyester polyols,polycarbonate polyols, polycaprolactone polyols, acrylic polyols, andother polyols. These polyols may be used either individually or incombinations of two or more. There are no specific limitations to themanner of polymerization of the structural units in these polyols. Anyof random polymerization, block polymerization, or graft polymerizationis acceptable.

Given as examples of the polyether polyols are polyethylene glycol,polypropylene glycol, polypropylene glycol-ethyleneglycol copolymer,polytetramethylene glycol, polyhexamethylene glycol, polyheptamethyleneglycol, polydecamethylene glycol, and polyether diols obtained byring-opening copolymerization of two or more ion-polymerizable cycliccompounds. Here, given as examples of the ion-polymerizable cycliccompounds are cyclic ethers such as ethylene oxide, isobutene oxide,tetrahydrofuran, 2-methyltetrahydrofuran, 3-methyltetrahydrofuran,dioxane, trioxane, tetraoxane, cyclohexene oxide, styrene oxide,epichlorohydrin, isoprene monoxide, vinyl oxetane, vinyltetrahydrofuran, vinyl cyclohexene oxide, phenyl glycidyl ether, butylglycidyl ether, and glycidyl benzoate. Specific examples of combinationsof two or more ion-polymerizable cyclic compounds include combinationsfor producing a binary copolymer such as tetrahydrofuran and2-methyltetrahydrofuran, tetrahydrofuran and 3-methyltetrahydrofuran,and tetrahydrofuran and ethylene oxide; and combinations for producing aternary copolymer such as a combination of tetrahydrofuran,2-methyltetrahydrofuran, and ethylene oxide, a combination oftetrahydrofuran, butene-1-oxide, and ethylene oxide, and the like. Thering-opening copolymers of these ion-polymerizable cyclic compounds maybe either random copolymers or block copolymers.

Included in these polyether polyols are products commercially availableunder the trademarks, for example, PTMG1000, PTMG2000 (manufactured byMitsubishi Chemical Corp.), PEG#1000 (manufactured by Nippon Oil andFats Co., Ltd.), PTG650 (SN), PTG1000 (SN), PTG2000 (SN), PTG3000,PTGL1000, PTGL2000 (manufactured by Hodogaya Chemical Co., Ltd.),PEG400, PEG600, PEG1000, PEG1500, PEG2000, PEG4000, PEG6000(manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) and Pluronics (byBASF).

Polyester diols obtained by reacting a polyhydric alcohol and apolybasic acid are given as examples of the polyester polyols. Asexamples of the polyhydric alcohol, ethylene glycol, polyethyleneglycol, tetramethylene glycol, polytetramethylene glycol,1,6-hexanediol, 3-methyl-1,5-pentanediol, 1,9-nonanediol,2-methyl-1,8-octanediol, and the like can be given. As examples of thepolybasic acid, phthalic acid, dimer acid, isophthalic acid,terephthalic acid, maleic acid, fumaric acid, adipic acid, sebasic acid,and the like can be given.

These polyester polyol compounds are commercially available under thetrademarks such as MPD/IPA500, MPD/IPA1000, MPD/IPA2000, MPD/TPA500,MPD/TPA1000, MPD/TPA2000, Kurapol A-1010, A-2010, PNA-2000, PNOA-1010,and PNOA-2010 (manufactured by Kuraray Co., Ltd.).

As examples of the polycarbonate polyols, polycarbonate ofpolytetrahydrofuran, poly(hexanediol carbonate), poly(nonanediolcarbonate), poly(3-methyl-1,5-pentamethylene carbonate), and the likecan be given.

As commercially available products of these polycarbonate polyols,DN-980, DN-981 (manufactured by Nippon Polyurethane Industry Co., Ltd.),Priplast 3196, 3190, 2033 (manufactured by Unichema), PNOC-2000,PNOC-1000 (manufactured by Kuraray Co., Ltd.), PLACCEL CD220, CD210,CD208, CD205 (manufactured by Daicel Chemical Industries, Ltd.),PC-THF-CD (manufactured by BASF), and the like can be given.

Polycaprolactone diols obtained by reacting e-caprolactone and a diolcompound are given as examples of the polycaprolactone polyols having amelting point of 0° C. or higher. Here, given as examples of the diolcompound are ethylene glycol, polyethylene glycol, polypropylene glycol,polypropylene glycol, tetramethylene glycol, polytetramethylene glycol,1,2-polybutylene glycol, 1,6-hexanediol, neopentyl glycol,1,4-cyclohexanedimethanol, 1,4-butanediol, and the like.

Commercially available products of these polycaprolactone polyolsinclude PLACCEL 240, 230, 230ST, 220, 220ST, 220NP1, 212, 210, 220N,210N, L230AL, L220AL, L220PL, L220PM, L212AL (all manufactured by DaicelChemical Industries, Ltd.), Rauccarb 107 (by Enichem), and the like.

As examples of other polyols ethylene glycol, 1,4-butanediol,1,5-pentanediol, 1,6-hexanediol, polyoxyethylene bisphenol A ether,polyoxypropylene bisphenol A ether, polyoxyethylene bisphenol F ether,polyoxypropylene bisphenol F ether, and the like can be given.

As these other polyols, those having a alkylene oxide structure in themolecule, in particular polyether polyols, are preferred. Specifically,polyols containing polytetramethylene glycol and copolymer glycols ofbutyleneoxide and ethyleneoxide are particularly preferred.

The reduced number average molecular weight derived from the hydroxylnumber of these polyols is usually from about 50 to about 15,000, andpreferably from about 1,000 to about 8,000.

Given as examples of the polyisocyanate used for the oligomer are2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 1,3-xylylenediisocyanate, 1,4-xylylene diisocyanate, 1,5-naphthalene diisocyanate,m-phenylene diisocyanate, p-phenylene diisocyanate,3,3′-dimethyl-4,4′-diphenylmethane diisocyanate, 4,4′-diphenylmethanediisocyanate, 3,3′-dimethylphenylene diisocyanate, 4,4′-biphenylenediisocyanate, 1,6-hexane diisocyanate, isophorone diisocyanate,methylenebis(4-cyclohexylisocyanate), 2,2,4-trimethylhexamethylenediisocyanate, bis(2-isocyanato-ethyl)fumarate, 6-isopropyl-1,3-phenyldiisocyanate, 4-diphenylpropane diisocyanate, hydrogenateddiphenylmethane diisocyanate, hydrogenated xylylene diisocyanate,tetramethyl xylylene diisocyanate, lysine isocyanate, and the like.These polyisocyanate compounds may be used either individually or incombinations of two or more. Preferred polyisocyanates are isophoronediisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4-tolylenediisocyanate, and 2,6-tolylene diisocyanate.

Examples of the hydroxyl group-containing (meth)acrylate used in theoligomer, include, (meth)acrylates derived from (meth)acrylic acid andepoxy and (meth)acrylates comprising alkylene oxides, more inparticular, 2-hydroxy ethyl (meth)acrylate, 2-hydroxypropylacrylate and2-hydroxy-3-oxyphenyl(meth)acrylate. Acrylate functional groups arepreferred over methacrylates.

The ratio of polyol, polyisocyanate, and hydroxyl group-containing(meth)acrylate used for preparing the urethane (meth)acrylate isdetermined so that about 1.1 to about 3 equivalents of an isocyanategroup included in the polyisocyanate and about 0.1 to about 1.5equivalents of a hydroxyl group included in the hydroxylgroup-containing (meth)acrylate are used for one equivalent of thehydroxyl group included in the glycol.

In the reaction of these three components, a urethanization catalystsuch as copper naphthenate, cobalt naphthenate, zinc naphthenate,di-n-butyl tin dilaurate, triethylamine, andtriethylenediamine-2-methyltriethyleneamine, is usually used in anamount from about 0.01 to about 1 wt % of the total amount of thereactant. The reaction is carried out at a temperature from about 10 toabout 90° C., and preferably from about 30 to about 80° C.

The number average molecular weight of the urethane (meth)acrylate usedin the composition of the present invention is preferably in about 500or higher, more preferably 800 or higher, and particularly preferred1,200 g/mol or higher. Generally, the molecular weight is about 20,000g/mol or lower, and more preferably about 10,000 g/mol or lower. If thenumber average molecular weight of the urethane (meth)acrylate is lessthan about 100 g/mol, the resin composition tends to solidify; on theother hand, if the number average molecular weight is larger than about20,000 g/mol, the viscosity of the composition becomes high, makinghandling of the composition difficult. Particularly preferred for outerprimary coatings inks or matrix materials are oligomers having a numberaverage molecular weight between about 800 and about 4,000 g/mol.

The urethane (meth)acrylate is used in an amount of 5% or more,preferably from about 10 wt % or more, and more preferably from about 20wt % or more, of the total amount of the resin composition. Generally,the amount of urethane(meth)acrylate oligomer is about 90% or less,preferably about 80 wt % or less. When the composition is used as acoating material for optical fibers, the range from about 20 to about 80wt % is particularly preferable to ensure excellent coatability, as wellas superior flexibility and long-term reliability of the cured coating.

Other oligomers that can be used include polyester (meth)acrylate, epoxy(meth)acrylate, polyamide (meth)acrylate, siloxane polymer having a(meth)acryloyloxy group, a reactive polymer obtained by reacting(meth)acrylic acid and a copolymer of glycidyl methacrylate and otherpolymerizable monomers, and the like. Particularly preferred arebisphenol A based acrylate oligomers such as alkoxylatedbisphenol-A-diacrylate and diglycidyl-bisphenol-A-diacrylate.

Beside the above-described components, other curable oligomers orpolymers may be added to the liquid curable resin composition of thepresent invention to the extent that the characteristics of the liquidcurable resin composition are not adversely affected.

Preferred oligomers are polyether based acrylate oligomers,polycarbonate acrylate oligomers, polyester acrylate oligomers, alkydacrylate oligomers and acrylated acrylic oligomers. More preferred arethe urethane-containing oligomers thereof. Even more preferred arepolyether urethane acrylate oligomers and urethane acrylate oligomersusing blends of the above polyols, and particularly preferred arealiphatic polyether urethane acrylate oligomers. The term “aliphatic”refers to a wholly aliphatic polyisocyanate used. However, alsourethane-free acrylate oligomers, such as urethane-free acrylatedacrylic oligomers, urethane-free polyester acrylate oligomers andurethane-free alkyd acrylate oligomers are also preferred.

(B) Reactive Diluent

Suitable reactive diluents include those exemplified herein below.

Polymerizable vinyl monomers such as polymerizable monofunctional vinylmonomers containing one polymerizable vinyl group in the molecule andpolymerizable polyfunctional vinyl monomers containing two or morepolymerizable vinyl groups in the molecule may be added to the liquidcurable resin composition of the present invention.

Given as specific examples of the polymerizable monofunctional vinylmonomers are vinyl monomers such as N-vinyl pyrrolidone, N-vinylcaprolactam, vinyl imidazole, and vinyl pyridine; (meth)acrylatescontaining an alicyclic structure such as isobornyl (meth)acrylate,bornyl (meth)acrylate, tricyclodecanyl (meth)acrylate, dicyclopehtanyl(meth)acrylate, dicyclopentenyl (meth)acrylate, and cyclohexyl(meth)acrylate; benzyl (meth)acrylate, 4-butylcyclohexyl (meth)acrylate,acryloylmorpholine, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl(meth)acrylate, 2-hydroxybutyl (meth)acrylate, methyl (meth)acrylate,ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate,butyl (meth)acrylate, amyl (meth)acrylate, isobutyl (meth)acrylate,t-butyl (meth)acrylate, pentyl (meth)acrylate, isoamyl (meth)acrylate,hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate,isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl(meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl(meth)acrylate, dodecyl (meth)acrylate, lauryl (meth)acrylate, stearyl(meth)acrylate, isostearyl (meth)acrylate, tetrahydrofurfuryl(meth)acrylate, butoxyethyl (meth)acrylate, ethoxydiethylene glycol(meth)acrylate, benzyl(meth)acrylate, phenoxyethyl(meth)acrylate,polyethylene glycol mono(meth)acrylate, polypropylene glycolmono(meth)acrylate, methoxyethylene glycol (meth)acrylate, ethoxyethyl(meth)acrylate, methoxypolyethylene glycol (meth)acrylate,methoxypropylene glycol (meth)acrylate, diacetone(meth)acrylamide,isobutoxy methyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide,t-octyl(meth)acrylamide, dimethylaminoethyl (meth)acrylate,diethylaminoethyl (meth)acrylate, 7-amino-3,7-dimethyloctyl(meth)acrylate, N,N-diethyl(meth)acrylamide, N,N-dimethyl aminopropyl(meth)acrylamide, hydroxy butyl vinyl ether, lauryl vinyl ether,cetyl vinyl ether, 2-ethylhexyl vinyl ether, acrylate monomers shown bythe following formulas (1) to (3),

wherein R⁷ is a hydrogen atom or a methyl group, R⁸ is an alkylene grouphaving 2-6, and preferably 2-4 carbon atoms, R⁹ is a hydrogen atom or anorganic group containing 1-12 carbon atoms or an aromatic ring, and r isan integer from 0 to 12, and preferably from 1 to 8,

wherein R⁷ is the same as defined above, R¹⁰ is an alkylene group having2-8, and preferably 2-5 carbon atoms, and q is an integer from 1 to 8,and preferably from 1 to 4,

wherein R⁷, R¹⁰, and q are the same as defined above.

As examples of commercially available products of the polymerizablemonofunctional vinyl monomers, Aronix M102, M110, M111, M113, M117(manufactured by Toagosei Co., Ltd.), LA, IBXA, Viscoat #190, #192,#2000 (manufactured by Osaka Organic Chemical Industry Co., Ltd.), LightAcrylate EC-A, PO-A, NP-4EA, NP-8EA, M-600A, HOA-MPL (manufactured byKyoeisha Chemical Co., Ltd.), KAYARAD TC110S, R629, R644 (manufacturedby Nippon Kayaku Co., Ltd.), and the like can be given.

Given as examples of the polymerizable polyfunctional vinyl monomers arethe following acrylate compounds: trimethylolpropane tri(meth)acrylate,pentaerythritol tri(meth)acrylate, ethylene glycol di(meth)acrylate,tetraethylene glycol di(meth)acrylate, polyethylene glycoldi(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanedioldi(meth)acrylate, neopentyl glycol di(meth)acrylate,trimethylolpropanetrioxyethyl (meth)acrylate,tris(2-hydroxyethyl)isocyanurate tri(meth)acrylate,tris(2-hydroxyethyl)isocyanurate di(meth)acrylate,bis(hydroxymethyl)tricyclodecane di(meth)acrylate, di(meth)acrylate of adiol which is an addition compound of ethylene oxide or propylene oxideto bisphenol A, di(meth)acrylate of a diol which is an addition compoundof ethylene oxide or propylene oxide to hydrogenated bisphenol A,epoxy(meth)acrylate obtained by the addition of (meth)acrylate todiglycidyl ether of bisphenol A, diacrylate of polyoxyalkylene bisphenolA, and triethylene glycol divinyl ether.

Examples of commercially available products of the polymerizablepolyfunctional vinyl monomers include Yupimer UV SA1002, SA2007(manufactured by Mitsubishi Chemical Corp.), Viscoat #195, #230, #215,#260, #335HP, #295, #300, #700 (manufactured by Osaka Organic ChemicalIndustry Co., Ltd.), Light Acrylate 4EG-A, 9EG-A, NP-A, DCP-A, BP-4EA,BP-4PA, PE-3A, PE-4A, DPE-6A (manufactured by Kyoeisha Chemical Co.,Ltd.), KAYARAD R-604, DPCA-20,-30,-60,-120, HX-620, D-310, D-330(manufactured by Nippon Kayaku Co., Ltd.), Aronix M-208, M-210, M,-215,M-220, M-240, M-305, M-309, M-315, M-325 (manufactured by Toagosei Co.,Ltd.), and the like.

These polymerizable vinyl monomers are used in an amount from about 10to about 70 wt %, and preferably from about 15 to about 60 wt %, of thetotal amount of the resin composition. If the amount is less than about10 wt %, the viscosity of the composition is so high that coatability isimpaired. The amount exceeding about 70 wt % may result in not only anincreased cure shrinkage, but also insufficient toughness of the curedproducts.

Preferred reactive diluents include alkoxylated alkyl substituted phenolacrylate, such as ethoxylated nonyl phenol acrylate, vinyl monomers suchas vinyl caprolactam, isodecyl acrylate, and alkoxylated bisphenol Adiacrylate such as ethoxylated bisphenol A diacrylate.

(C) Specific Combination of Components

Preferably, the present compositions comprise:

-   -   (i) a component represented by the following formula (a)        A-X₁-A  (a)    -    wherein        -   A represents a (meth)acrylate group, preferably an acrylate            group; and        -   X₁ represents an aliphatic or aromatic group, preferably            having a molecular weight below 750, more preferably below            500, most preferably less than 350 g/mol; and    -   (ii) a urethane (meth)acrylate component comprising a        (metha)acrylate group (preferably an acrylate group), X₁, and a        residue of a multifunctional isocyanate (preferably a residue of        a diisocyanate).

Component (ii) may be a urethane (meth)acrylate component represented bythe following formula (b);X₂—I—X₂  (b)

-   -   wherein I represents a diisocyanate residue and X₂ represents a        residue of a component represented by the following formula (c):        A-X₁—OH  (c).

Accordingly, X₂ represents a residue of a hydroxyfunctional(meth)acrylate.

Preferably X₁ comprises one or more aromatic rings, preferably 2aromatic rings. The one or more aromatic rings are preferably present inX₁ as phenolic residues. It is also preferred that X₁ comprises one ormore alkoxy groups (e.g. 1-20, 1-10, or 2-6 alkoxy groups), for instanceethoxy and/or propoxy groups.

Preferably, A-X₁-A represents a bisphenol diacrylate, for instance abisphenol A diacrylate such as an alkoxylated (e.g. ethoxylated and/orpropoxylated) bisphenol A diacrylate.

Component (ii) may be prepared by reacting at least part of thehydroxyfunctional side-products, that may be present in a sample ofA-X₁-A, with one or more suitable diisocyanates. Therewith,hydroxyfunctional impurities (side products) can be converted intodifunctional components. This conversion may be done in situ, i.e. bysimply adding diisocyanate to a composition comprising severalcomponents, one of which being a component represented by A-X₁-A. Theconversion may also be effected by first adding diisocyanate to a sampleof A-X₁-A, reacting diisocyanate with hydroxyfunctional impuritiespresent in the sample, and then adding the sample to the composition.

Suitable diisocyanates include, for example 2,4-tolylene diisocyanate,2,6-tolylene diisocyanate, 1,3-xylylene diisocyanate, 1,4-xylylenediisocyanate, 1,5-naphthalene diisocyanate, m-phenylene diisocyanate,p-phenylene diisocyanate, 3,3′-dimethyl-4,4′-diphenylmethanediisocyanate, 4,4′-diphenylmethane diisocyanate, 3,3′-dimethylphenylenediisocyanate, 4,4′-biphenylene diisocyanate, 1,6-hexane diisocyanate,isophorone diisocyanate, methylenebis(4-cyclohexylisocyanate),2,2,4-trimethylhexamethylene diisocyanate,bis(2-isocyanato-ethyl)fumarate, 6-isopropyl-1,3-phenyl diisocyanate,4-diphenylpropane diisocyanate, hydrogenated diphenylmethanediisocyanate, hydrogenated xylylene diisocyanate, tetramethyl xylylenediisocyanate, lysine isocyanate, and the like. These polyisocyanatecompounds may be used either individually or in combinations of two ormore. Preferred polyisocyanates include aromatic isocyanates,particularly tolylene diisocyanates.

(D) Photoinitiator

When the liquid curable resin composition of the present invention iscured by radiation, a photo-polymerization initiator is used.

In a preferred embodiment of the present invention, the photoinitiators(Ci) are free radical photoinitiators.

Free-radical photoinitiators are generally divided into two classesaccording to the process by which the initiating radicals are formed.Compounds that undergo unimolecular bond cleavage upon irradiation aretermed Type I or homolytic photoinitiators, as shown by formula (1):

Depending on the nature of the functional group and its location in themolecule relative to the carbonyl group, the fragmentation can takeplace at a bond adjacent to the carbonyl group (α-cleavage), at a bondin the β-position (β-cleavage) or, in the case of particularly weakbonds (like C—S bonds or O—O bonds), elsewhere at a remote position. Byfar the most important fragmentation in photoinitiator molecules is theα-cleavage of the carbon-carbon bond between the carbonyl group and thealkyl residue in alkyl aryl ketones which is known as the Norrish Type Ireaction.

If the excited state photoinitiator interacts with a second molecule (acoinitiator COI) to generate radicals in a bimolecular reaction as shownby formula (2), the initiating system is termed a Type IIphotoinitiator. In general, the two main reaction pathways for Type IIphotoinitiators are hydrogen abstraction by the excited initiator orphotoinduced electron transfer, followed by fragmentation. Bimolecularhydrogen abstraction is a typical reaction of diary ketones.Photoinduced electron transfer is a more general process which is notlimited to a certain class of compounds.

Examples of suitable Type I homolytic free-radical photoinitiators arebenzoin derivatives, methylolbenzoin and 4-benzoyl-1,3-dioxolanederivatives, benzilketals, α,α-dialkoxyacetophenones, a-hydroxyalkylphenones, α-aminoalkylphenones, acylphosphine oxides,bisacylphosphine oxides, acylphosphine sulphides halogenatedacetophenone derivatives, and the like. Commercial examples of suitableType I photoinitiators are Irgacure 651 (benzildimethyl ketal or2,2-dimethoxy-1,2-diphenylethanone, Ciba-Geigy),

Irgacure 184 (1-hydroxy-cyclohexyl-phenyl ketone as the activecomponent, Ciba-Geigy),

Darocur 1173 (2-hydroxy-2-methyl-1-phenylpropan-1-one as the activecomponent, Ciba-Geigy),

Irgacure 907 (2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, Ciba-Geigy),

Irgacure 369(2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butan-1-one as theactive component, Ciba-Geigy),

Esacure KIP 150 (poly{2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propan-1-one}, FratelliLamberti),

Esacure KIP 100 F (blend of poly{2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propan-1-one} and2-hydroxy-2-methyl-1-phenyl-propan-1-one, Fratelli Lamberti),

Esacure KTO 46 (blend of poly{2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propan-1-one},2,4,6-trimethylbenzoyldiphenylphosphine oxide and methylbenzophenonederivatives, Fratelli Lamberti),

acylphosphine oxides such as Lucirin TPO (2,4,6-trimethylbenzoyldiphenyl phosphine oxide, BASF),

Irgacure 819 (bis (2,4,6-trimethylbenzoyl)-phenyl-phosphine-oxide,Ciba-Geigy),

Irgacure 1700 (25:75% blend of bis(2,6-dimethoxybenzoyl)2,4,4-trimethylpentyl phosphine oxide and2-hydroxy-2-methyl-1-phenyl-propan-1-one, Ciba-Geigy), and the like.Also mixtures of type I photoinitiators can be used. For colored (e.g.pigmented) systems, phosphine oxide type photoinitiators and Irgacure907 are preferred.

Examples of suitable Type-II (hydrogen abstraction) photoinitiators arearomatic ketones such as benzophenone, xanthone, derivatives ofbenzophenone (e.g. chlorobenzophenone), blends of benzophenone andbenzophenone derivatives (e.g. Photocure 81, a 50/50 blend of4-methyl-benzophenone and benzophenone), Michler's Ketone, EthylMichler's Ketone, thioxanthone and other xanthone derivatives likeQuantacure ITX (isopropyl thioxanthone), benzil, anthraquinones (e.g.2-ethyl anthraquinone), coumarin, and the like. Chemical derivatives andcombinations of these photoinitiators can also be used.

Type-II photoinitiators generally are used together with an aminesynergist. Preferably, the amine synergist is chosen from the groupconsisting of a monomer tertiary amine compound, an oligomer (polymer)tertiary amine compound, a polymerizable amino acrylate compound, apolymerized amino acrylate compound and mixtures thereof.

The amine-synergist may include tertiary amine compounds, such asalkanol-dialkylamines (e.g., ethanol-diethylamine), alkyldialkanolamines(e.g. methyldiethanolamine), trialkanolamines (e.g. triethanolamine),and ethylenically unsaturated amine-functional compounds includingamine-functional polymer compounds, copolymerizable amine acrylates, andthe like. The ethylenically unsaturated amine compounds may also includedialkylamino alkyl(meth)acrylates (e.g., diethylaminoethylacrylate) orN-morpholinoalkyl-(meth)acrylates (e.g., N-morpholinoethyl-acrylate).

Preferably, the total amount of photoinitiators present is between about0.10 wt. % and about 20.0 wt. % relative to the total amount of thecoating composition. More preferably, the total amount is at least about0.5 wt. %, particularly preferred, at least about 1.0 wt. %, and mostpreferred, at least about 2.0 wt. %. Moreover, the total amount ispreferably less than about 15.0 wt. %, more preferably, less than about10.0 wt. %, and particularly preferred, less than about 6.0 wt. %

Preferably, each of the photoinitiators (Ci) is individually present inan amount of at least about 0.02 wt. %, more preferably, at least about0.05 wt. %, particularly preferred, at least about 0.1 wt. %, and mostpreferred, at least about 0.15 wt. %. Further, each photoinitiator (Ci)is individually preferably present in an amount of about 10.0 wt. % orless, more preferably, about 5.0 wt. % or less, particularly preferably,about 4.0 wt. % or less, and most preferred, about 2.5 wt. % or less.

The ratio C_(i):C of the amount of individual photoinitiator (Ci) to thetotal amount of photoinitiators (C) preferably is about 50% or less,more preferably about 45% or less, particularly preferred about 40% orless, most preferred about 30% or less. The ratio C_(i):C preferably isat least about 2%, more preferably at least about 5%, particularlypreferred at least about 10%.

It is preferred that at least two of the compounds (Ci) are homolyticfree radical photoinitiators, preferably, at least three, morepreferably, at least four, particularly preferred all the compounds (Ci)are homolytic free radical photoinitiators. Moreover, it is preferredthat at least two of the compounds (Ci) are α-cleavage homolytic freeradical photoinitiators, more preferred, at least three, particularlypreferred at least four and most preferred, all of the compounds (Ci)are of the α-cleavage type.

In one preferred embodiment of the present invention at least one of thephotoinitiators contains a phosphorous, sulfur or nitrogen atom. It iseven more preferred that the photoinitiator package comprises at least acombination of a photoinitiator containing a phosphorous atom and aphotoinitiator containing a sulfur atom.

In another preferred embodiment of the invention, at least one of thecompounds (Ci) is an oligomeric or polymeric photoinitiator. Besidesshowing an improved cure speed, said coating compositions comprising atleast one polymeric photoinitiator (Ci) additionally exhibit, upon cure,improved release properties from another covering layer, such as amatrix or bundling material or any other material applied to the surfaceof the subject composition.

The oligomeric photoinitiator can include Esacure KIP 100F, availableform Sartomer Corporation.

(E) Additives

An amine compound can be added to the liquid curable resin compositionof the present invention to prevent generation of hydrogen gas, whichcauses transmission loss in the optical fibers. As examples of the aminewhich can be used here, diallylamine, diisopropylamine, diethylamine,diethylhexylamine, and the like can be given.

In addition to the above-described components, various additives such asantioxidants, UV absorbers, light stabilizers, silane coupling agents,coating surface improvers, heat polymerization inhibitors, levelingagents, surfactants, colorants, preservatives, plasticizers, lubricants,solvents, fillers, aging preventives, and wettability improvers can beused in the liquid curable resin composition of the present invention,as required. Examples of antioxidants include Irganox 1010, 1035, 1076,1222 (manufactured by Ciba Specialty Chemicals Co., Ltd.), Antigene P,3C, FR, Sumilizer GA-80 (manufactured by Sumitomo Chemical IndustriesCo., Ltd.), and the like; examples of UV absorbers include Tinuvin P,234, 320, 326, 327, 328, 329, 213 (manufactured by Ciba SpecialtyChemicals Co., Ltd.), Seesorb 102, 103, 110, 501, 202, 712, 704(manufactured by Sypro Chemical Co., Ltd.), and the like; examples oflight stabilizers include Tinuvin 292, 144, 622LD (manufactured by CibaSpecialty Chemicals Co., Ltd.), Sanol LS770 (manufactured by Sankyo Co.,Ltd.), Sumisorb TM-061 (manufactured by Sumitomo Chemical IndustriesCo., Ltd.), and the like; examples of silane coupling agents includeaminopropyltriethoxysilane, mercaptopropyltrimethoxy-silane, andmethacryloxypropyltrimethoxysilane, and commercially available productssuch as SH6062, SH6030 (manufactured by Toray-Dow Corning Silicone Co.,Ltd.), and KBE903, KBE603, KBE403 (manufactured by Shin-Etsu, ChemicalCo., Ltd.); examples of coating surface improvers include siliconeadditives such as dimethylsiloxane polyether and commercially availableproducts such as DC-57, DC-190 (manufactured by Dow-Corning), SH-28PA,SH-29PA, SH-30PA, SH-190 (manufactured by Toray-Dow Corning SiliconeCo., Ltd.), KF351, KF352, KF353, KF354 (manufactured by Shin-EtsuChemical Co., Ltd.), and L-700, L-7002, L-7500, FK-024-90 (manufacturedby Nippon Unicar Co., Ltd.).

The description on radiation curable compositions can also apply tocolored compositions, being either a colored single, inner primary, orouter primary composition, an ink composition or a colored matrix orbundling material. The colorant can be a pigment or dye. The pigment canbe any pigment suitable for use in pigmented colored optical fibercoatings. Preferably, the pigment is in the form of small particles andis capable of withstanding UV-radiation.

Pigments can be conventional or organic pigments as disclosed in, forexample, Ullman's Encyclopedia of Industrial Chemistry, 5^(th) Ed., Vol.A22, VCH Publishers (1993), pages 154-155, the complete disclosure ofwhich is hereby fully incorporated by reference. The pigment can beselected based on, for example, whether the composition is a coloredsecondary, ink coating or matrix material. Ink coatings are typicallymore heavily pigmented.

General classes of suitable colorants include, among others, inorganicwhite pigments, black pigments; iron oxides; chronium oxide greens; ironblue and chrome green; violet pigments; ultramarine pigments; blue,green, yellow, and brown metal combinations; lead chromates and leadmolybdates; cadmium pigments; titane pigments; pearlescent pigments;metallic pigments; monoazo pigments, diazo pigments; diazo condensationpigments; quinacridone pigments, dioxazine violet pigment; vat pigments;perylene pigments; thioindigo pigments; phthalocyanine pigments; andtetrachloroindolinones; azo dyes; anthraquinone dyes; xanthene dyes; andazine dyes. Fluorescent pigments can also be used.

Preferably, the pigment has a mean particle size of not more than about1 μm. The particle size of the commercial pigments can be lowered bymilling if necessary. The pigment is preferably present in an amount ofabout 0.1 to about 10% by weight, and more preferably in an amount ofabout 0.3 to about 8% by weight.

Instead of pigments also dyes can be used if sufficiently color stable.Reactive dyes are particularly preferred. Suitable dyes includepolymethine dyes, di and triarylmethine dyes, aza analogues ofdiarylmethine dyes, aza (18) annulenes (or natural dyes), nitro andnitroso dyes, aza dyes, anthraquinone dyes and sulfur dyes. These dyesare well known in the art.

All these additives may be added to the compositions according to theinvention in an amount that is usual for the additive when used inoptical fiber coatings.

Physical Characteristics

The viscosity of the liquid curable resin composition of the presentinvention is usually in the range from about 200 to about 20,000 cps at25° C., and preferably from about 2,000 to about 15,000.

The radiation curable composition of the present invention may beformulated to be used as a single coating, an inner primary coating,outer primary coating, a matrix material or bundling material (all ofwhich can be colored or not), or as an ink. The invention isparticularly suitable for harder materials such as coatings, inks ormatrix materials having modulus of about 400 MPa or higher, morepreferably 600 MPa or higher and most preferably 800 MPa or higher. Inparticular, the radiation-curable compositions of the present inventionmay be formulated such that the composition after cure has a modulus aslow as 0.1 MPa and as high as 2,000 MPa or more. Those having a modulusin the lower range, for instance, from 0.1 to 10 MPa, preferably 0.1 to5 MPa, and more preferably 0.5 to less than 3 MPa are typically suitablefor inner primary coatings for fiber optics. In contrast, suitablecompositions for outer primary coatings, inks and matrix materialsgenerally have a modulus of above 50 MPa, with outer primary coatingstending to have a modulus more particularly above 100 up to 2,500 MPaand matrix materials tending to be more particularly between about 50MPa to about 200 MPa for soft matrix materials, and between 200 to about2,500 MPa for hard matrix materials. The radiation-curable compositionof the present invention may be formulated such that the compositionafter cure has a Tg between −70° C. and 130° C. The Tg is measured asthe peak tan-delta in a DMA curve. Preferably, for harder materials, theTg is about 40° C. or higher, more preferably, about 60° C. or higher.

Elongation and tensile strength of these materials can also be optimizeddepending on the design criteria for a particular use. For curedcoatings formed from radiation-curable compositions formulated for useas inner primary coatings on optical fibers, the elongation-at-break istypically greater than 65%, preferably greater than 80%, more preferablythe elongation-at-break is at least 110%, more preferably at least 150%but not typically higher than 400%. For coatings formulated for outerprimary coatings, inks and matrix materials the elongation-at-break istypically between 6% and 100%, and preferably higher than 10%, morepreferably about 20% or higher and in particular about 25% or higher.

In one preferred embodiment of the invention, polyfunctional isocyanatesare added to the otherwise final coating composition, and the mixture isstirred for obtaining a homogeneous mixture. Hydroxyfunctionalcomponents are in this way reacted with each other, and, apparently,this leads to improved mechanical properties.

In another preferred embodiment, specific components know to comprisehydroxyfunctional compounds are reacted with polyfunctional isocyanates,and, thereafter, these components are added to the coating composition.This also gives an improvement in mechanical properties.

In yet another embodiment, the specific components known to comprisehydroxy functional compounds are reacted with a both polyisocyanates andhydroxyfunctional acrylate compounds, so obtaining further oligomericcompounds that yield improved mechanical properties.

A preferred hydroxyfunctional component is alkoxylated bisphenol-A oralkoxylated bispheno/-A-mono acrylate. Polyfunctioal isocyanates andhydroxyfunctional acrylate compounds as described above are particularlyuseful. Useful amounts of these toughening agents are, for instance, 10wt % or less, e.g. 5 wt % or less, relative to the total composition.This means that generally 0.2-5% by wt. polyisocyanate is used,preferably 0.3-3% by wt., to achieve the toughening.

Preferred applications for the present compositions are in the field ofoptical fiber coatings, such as, for instance, matrix materials,bundling materials, secondary coatings, colored secondary coatings, andinks.

EXAMPLES

The following examples are given as particular embodiments of theinvention and to demonstrate the practice and advantages thereof. Theexamples are given by way of illustration and are not intended to limitthe specification or claims.

Tensile Strength, Elongation, Modulus, and Toughness Test Method

The tensile strength, elongation and secant modulus of cured samples wastested using a universal testing instrument, Instron Model 4201 equippedwith a personal computer and software “Series IX Materials TestingSystem.” The load cells used were 2 and 20 pound capacity. The ASTMD638M was followed, with the following modifications.

A drawdown of each material to be tested was made on glass plate orMylar (in particular, the outer primary coating compositions, unlessotherwise noted, were measured on Mylar) and cured using a UV processor.The cured film was conditioned at 22 to 24° C. and 50±5% relativehumidity for a minimum of sixteen hours prior to testing.

A minimum of eight test specimens, having a width of 0.5±0.002 inchesand a length of 5 inches, were cut from the cured film. To minimize theeffects of minor sample defects, sample specimens were cut parallel tothe direction in which the drawdown of the cured film was prepared. Ifthe cured film was tacky to the touch, a small amount of talc wasapplied to the film surface using a cotton tipped applicator.

The test specimens were then removed from the substrate. Caution wasexercised so that the test specimens were not stretched past theirelastic limit during the removal from the substrate. If any noticeablechange in sample length had taken place during removal from thesubstrate, the test specimen was discarded.

If the top surface of the film was talc coated to eliminate tackiness,then a small amount of talc was applied to the bottom surface of testspecimen after removal from the substrate.

The average film thickness of the test specimens was determined. Atleast five measurements of film thickness were made in the area to betested (from top to bottom) and the average value used for calculations.If any of the measured values of film thickness deviates from theaverage by more than 10% relative, the test specimen was discarded. Allspecimens came from the same plate.

The appropriate load cell was determined by using the followingequation:[A×145]×0.0015=CWhere:

-   -   A=Product's maximum expected tensile strength (MPa);    -   145=Conversion Factor from MPa to psi;    -   0.00015=approximate cross-sectional area (in²) of test        specimens; and    -   C=lbs.        The 2 pound load cell was used for materials where C=1.8 lbs.        The 20 pound load cell was used for materials where 1.8<C<18        lbs. If C>19, a higher capacity load cell was required.

The crosshead speed was set to 1.00 inch/min (25.4 mm/min), and thecrosshead action was set to “return at break”. The crosshead wasadjusted to 2.00 inches (50.8 mm) jaw separation. The air pressure forthe pneumatic grips was turned on and adjusted as follows: setapproximately 20 psi (1.5 Kg/cm²) for primary optical fiber coatings andother very soft coatings; set approximately 40 psi (3 Kg/cm²) foroptical fiber single coats; and set approximately 60 psi (4.5 Kg/cm²)for secondary optical fiber coatings and other hard coatings. Theappropriate Instron computer method was loaded for the coating to beanalyzed.

After the Instron test instrument had been allowed to warm-up forfifteen minutes, it was calibrated and balanced following themanufacturer's operating procedures.

The temperature near the Instron Instrument was measured and thehumidity was measured at the location of the humidity gage. This wasdone just before beginning measurement of the first test specimen.

Specimens were only analyzed if the temperature was within the range23±1.0 C and the relative humidity was within 50±5%. The temperature wasverified as being within this range for each test specimen. The humidityvalue was verified only at the beginning and the end of testing a set ofspecimens from one plate.

Each test specimen was tested by suspending it into the space betweenthe upper pneumatic grips such that the test specimen was centeredlaterally and hanging vertically. Only the upper grip was locked. Thelower end of the test specimen was pulled gently so that it has no slackor buckling, and it was centered laterally in the space between the openlower grips. While holding the specimen in this position, the lower gripwas locked.

The sample number was entered and sample dimensions into the datasystem, following the instructions provided by the software package.

The temperature and humidity were measured after the last test specimenfrom the current drawdown was tested. The calculation of tensileproperties was performed automatically by the software package.

The values for tensile strength, % elongation, and secant, or segment,modulus were checked to determine whether any one of them deviated fromthe average enough to be an “outlier.” If the modulus value was anoutlier, it was discarded. If there were less than six data values forthe tensile strength, then the entire data set was discarded andrepeated using a new plate. The toughness was determined as the areaunder the stress-strain curve up to the elongation at break.

All, recorded values were normalized as shown below.

EXAMPLES

These examples illustrate the change observed in various physicalproperties of the below listed primary coating compositions, wherein anisocyanate is introduced either via a pre-mixture or in situ.

Outer Primary Coating Composition A (Approximate Percentages):Ethoxylated Bisphenol A Diacrylate (SR-349, Sartomer) 75% PolyetherUrethane Oligomer 20% Ethoxylated Nonylphenol Acrylate (SR-504D,Sartomer)  5% Hydroxycyclohexyl Phenyl Ketone (Irgacure-184) ˜1%2,4,6-Trimethylbenzoyl Diphenyl Phosphine Oxide <1% Thiodiethylene bis(3,5-di-tert-butyl-4-Hydroxy)hydrocinnamate <1%

Outer Primary Coating Composition B (Approximate Percentages):Ethoxylated Bisphenol A Diacrylate (SR-349, Sartomer) 56% PolyetherUrethane Oligomer 33% Ethoxylated Nonylphenol Acrylate (SR-504D,Sartomer)  6% Hydroxycyclohexyl Phenyl Ketone (Irgacure-184)  2%2,4,6-Trimethylbenzoyl Diphenyl Phosphine Oxide  1% Thiodiethylene bis(3,5-di-tert-butyl-4-Hydroxy) Hydrocinnamate <1%

Pre-Mixture Composition (Percent Based on Weight): Ethoxylated BisphenolA Diacrylate (SR-349, Sartomer) 94.3% Toluene Diisocyanate  3.7%2-Hydroxyethyl acrylate  1.9% Butylated Hydroxy Toluene 0.08% DibutyltinDilaurate 0.04%

TABLE 1 Relative Physical Properties of Composition A upon Addition ofthe Pre-Mixture Composition. Example 1 2 3 4 5 Composition A/Pre- 100/0.0  97.5/2.5   95/5.0 92.5/7.5    90/10.0 Mixture (wt/wt) RelativeTensile Strength 1.105 1.234 1.230 1.000 1 .054 Relative Elongation1.288 1.494 1.438 1.000 1.193 Relative Modulus 1.145 1.113 1.105 1.1051.000 Relative Toughness 1 .000 1.736 1.692 1.038 1.443Relative means that the lowest value in a category (tensile strength,elongation, modulus, or toughness) is normalized to 1.000, and that theother values are relative thereto.

TABLE 2 3/36 Relative Physical Properties of Composition A upon Additionof an Isocyanate Percent Isocyanate* 0 0.5 1 1.5 2 Relative TensileStrength TDI 1.181 1.183 1.341 1.371 1.181 TMDI 1.181 1.156 1.108 1.1001.000 IPDI 1.181 1.162 1.224 1.174 1.134 Relative Modulus TDI 1.0931.110 1.076 1.102 1.127 TMDI 1.093 1.102 1.000 1.059 1.068 IPDI 1.0930.966 1.068 1.051 1.025 Relative Elongation TDI 1.723 1.70  2.135 2.2502.554 TMDI 1.723 1.655 1.527 1.324 1.000 IPDI 1.723 1.932 1.757 1.7231.507 Relative Viscosity TDI 1.000 1.294 1.671 1.897 1.968 TMDI 1.0001.008 1.156 1.215 1.247 IPDI 1.000 1.021 1.026 1.215 1.273 RelativeToughness TDI 1.020 1.188 1.584 1.703 2.050 TMDI 1.020 1.129 0.990 0.9110.614 IPDI 1.020 1.356 1.248 1.178 1.000*Isocyanates used in this experiment were as follows: TolueneDiisocyanate (TDI); 2,2,4-Trimethyl Hexamethylene Diisocyanate (TMDI);and Isophorone Diisocyanate (IPDI). The indicated isocyanates were addedto Composition A and stirred at 70° C. for 1.5 h, prior to curing andtesting.

TABLE 3 Relative Physical Properties of Composition B upon Addition ofToluene Diisocyanate. Percent TDI 0 1 1.5 Relative Tensile Strength+HC,29 1.163 1.055 1.000 Relative Elongation 1.386 1.246 1.000 RelativeModulus 1.000 1.005 1.051 Relative Viscosity 1.000 1.437 1.553 RelativeToughness 1.471 1.245 1.000Toluene diisocyanate (TDI) was added to Composition B then heated to 70°C. for 1.5 h, prior to curing and testing.

1-21. (canceled)
 22. A method of improving the tensile strength,modulus, and/or elongation of a radiation-curable compositioncomprising: adding a multi-functional isocyanate to the compositionprior to curing.
 23. The method according to claim 22, furthercomprising reacting at least a portion of the added multi-functionalisocyanate with a hydroxyl-functional mono(meth)acrylate.
 24. Acomposition obtainable by the method according to any one of claims22-23.